1. Field of the Invention
The present invention relates to a circuit for encoding a composite image signal by synthesizing the composite image signal, especially for use in a television, and more particularly to a circuit and method for encoding a color television signal, which improves resolution of the display image and removes interference between a chrominance signal and a luminance signal by prefiltering with a pattern and motion adaptive variable bandwidth filter.
2. Background Art
Recently, digital signal processing techniques have been employed more frequently as a way to improve the quality of an image signal. Especially, in an IDTV (Improved Definition TV) and EDTV (Enhanced Definition TV) scheme, a motion adaptive signal processing technique has been used as a digital filter that separates a chrominance signal and a luminance signal, and a scanning line conversion circuit may be used to convert an interlaced scanning image signal with 525 scanning lines into a non-interlaced scanning image signal. By using the method stated above for a television receiver, it is possible to improve the resolution of the display image by efficiently removing cross luminance components which occur when a chrominance signal is mixed with a luminance signal, and cross color components which occur when a luminance signal is mixed with a chrominance signal.
A prior art device for achieving the improvements as stated above is shown in FIG. 1, wherein a luminance signal Y and the color difference signals R-Y (I) and B-Y (Q) are separated, respectively, from the red (R), green (G), and blue (B) color signals which are applied to a gamma correction matrix 4. The color difference signals I, Q are filtered by the corresponding low pass filters 10, 11 and modulated by a quadrature phase modulator 5 according to a chrominance sub-carrier signal 1 and a burst flag signal 2.
The signal output from the quadrature phase modulator 5 and the luminance signal Y from the gamma correction matrix 4 are combined at a mixer 6 according to an input signal 3 which is a synchronous and blocking pedestal signal. To obtain a resulting encoded video signal CV, the combined signal output from the mixer 6 is low-pass-filtered by the low pass filter 8.
Since the stated prior art is not a fundamental processing method which removes the cross luminance components from the luminance signal and the chrominance signal, low low quality resolution of the display image and interference of the image due to the cross-luminance components from the chrominance signal and the luminance signal often follow.